Chemical/mechanical polishing slurry, and chemical mechanical polishing process and shallow trench isolation process employing the same

ABSTRACT

A CMP oxide slurry includes an aqueous solution containing abrasive particles and two or more different passivation agents. Preferably, the aqueous solution is made up of deionized water, and the abrasive particles are a metal oxide selected from the group consisting of ceria, silica, alumina, titania, zirconia and germania. Also, a first passivation agent may be an anionic, cationic or nonionic surfactant, and a second passivation agent may be a phthalic acid and its salts. In one example, the first passivation agent is poly-vinyl sulfonic acid, and the second passivation agent is potassium hydrogen phthalate. The slurry exhibits a high oxide to silicon nitride removal selectivity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of and claims priority to application Ser. No.09/826,169, filed Apr. 5, 2001, now U.S. Pat. No. 6,540,935, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to chemical/mechanical polishing (CMP) ofmicroelectronic devices, and more particularly, the present inventionrelates to CMP slurries and-to fabrication processes employing CMPslurries.

2. Description of the Related Art

As the degree of integration of microelectronic devices continues toincrease, planarization processes used in the fabrication of suchdevices become more and more critical. That is, efforts to achievehighly integrated semiconductor devices are typically attended by thestacking of multiple interconnection and other layers on a semiconductorwafer. The resultant unevenness of the wafer surface presents a varietyof problems which are well-documented in the art. Planarizationprocesses are thus adopted at various stages of fabrication in an effortto minimize irregularities in the wafer surface.

One such planarization technique is chemical/mechanical polishing (CMP).In CMP, the wafer surface is pressed against a polishing pad in relativerotation. During polishing, an abrasive and chemically reactive solutionknown as a CMP slurry is made to flow into the polishing pad. This CMPtechnique planarizes the wafer surface by means of chemical and physicalreactions, that is, by supplying the chemically reactive slurry on apatterned surface of the wafer while at the same time physicallypressing the relative rotating surface of the polishing pad against thesurface of the wafer.

FIG. 1 is a schematic diagram showing a conventional example of a CMPapparatus used in the manufacture semiconductor devices. The illustratedCMP apparatus includes a polishing head 102, a polishing table 104, aslurry supply line 106 and a polishing pad 108. The CMP process iscarried out on the polishing table 104, having the polishing pad 108formed thereon. That is, while a slurry is supplied from a slurry supplyline 106, the polishing head 102 is made to rotate while pressing thesubstrate 100 against the polishing pad 108. In this manner, polishingis achieved.

One common application of CMP is in shallow trench isolation (STI). InSTI techniques, relatively shallow isolation trenches are formed, whichfunction as field regions used to separate active regions on a wafer. Aconventional example of an STI process is shown in FIGS. 2(a)-2(d). Inthis process, a pad oxide layer 202 and a silicon nitride (SiN) stoplayer 204 are sequentially stacked on a semiconductor substrate 200.Thereafter, a photoresist pattern (not shown) is formed atop the SiNstop layer 204. Then, using the photoresist as a mask, the SiN stoplayer 204, pad oxide layer 202 and the semiconductor substrate 200 arepartially etched to form a plurality of trenches 206 as shown in FIG.2(a). Subsequently, as shown in FIG. 2(b), an insulating oxide layer 208(which will ultimately form the trench oxide regions) is deposited so asto fill the trenches 206 and cover the surface of the SiN stop layer204. The oxide layer 208 is then subjected to CMP so as to remove theoxide layer 208 down to the level of the SiN stop layer 204. As aresult, the configuration of FIG. 2(c) is obtained. The SiN stop layer204 and the pad oxide layer 202 on the active regions are then removedvia an etching process. Thereafter, a gate oxide layer 210 is formed onthe surface of the semiconductor substrate 200 as shown in FIG. 2(d).

During the first-mentioned CMP process, the oxide layer 208 is removeduntil the upper surface of the SiN stop layer 204 is exposed. Due todiffering chemical and physical characteristics thereof, the oxide andSiN layers exhibit different removal rates when subjected to CMP usingknown slurries. The ratio of these removal rates at least partiallydefines the “selectivity” of the slurry being used. The lower theselectivity of the slurry, the more SiN that will be polished awayduring the CMP process.

Ideally, the CMP process would not remove any of the SiN layer, i.e.,the selectivity would be infinite. However, present CMP slurries exhibitlow selectivity (about 4 to 1, oxide to SiN), and thus polish the SiNlayer at unacceptably high rates. As a result, the SiN patterns may beirregularly removed during the CMP process, whereby thicknesses of theSiN patterns may vary across the wafer. This is especially problematicin the case where the semiconductor substrate has both densely andsparsely distributed patterns on the surface thereof. The end result isstep differences between the active and field regions when the formationof the field regions is complete. This can adversely affect subsequentdevice fabrication, which in turn can degrade transistor and devicecharacteristics, thus reducing process margins.

Hence, in the STI process, it is desirable that the SiN layer patternshave uniform thicknesses after removal of the oxide layer by CMP.However, uniformly thick SiN patterns are extremely difficult to achievesince present CMP slurries do not exhibit sufficient selectivity betweenthe oxide and SiN layers.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a CMP slurry whichexhibits improved removal selectivity between oxide and silicon nitridelayers.

It is a further object of the present invention to provide a CMP processwhich exhibits improved removal selectivity between oxide and siliconnitride layers.

It is still a further object of the present invention to provide an STIprocess which utilizes a CMP process having high removal selectivitybetween oxide and silicon nitride layers.

According to one aspect of the invention, a CMP slurry is provided whichincludes an aqueous solution containing abrasive particles and two ormore different passivation agents. Preferably, the aqueous solution ismade up of deionized water, and the abrasive particles are a metal oxideselected from the group consisting of ceria, silica, alumina, titania,zirconia and germania. Also, a first passivation agent may be ananionic, cationic or nonionic surfactant, and a second passivation agentmay be a phthalic acid. In one example, the first passivation agent ispoly-vinyl sulfonic acid, and the second passivation agent is potassiumhydrogen phthalate.

The aqueous solution forming the CMP slurry may also include a removalrate accelerator, such as ammonium hydrogen phosphate. The aqueoussolution may further include a pH controller for controlling a pHthereof.

In another aspect of the invention, a CMP method is provided in which asurface of a semiconductor wafer is made to contact a surface of apolishing pad, an aqueous solution containing abrasive particles anddifferent first and second passivation agents is supplied to aninterface between the surface of the polishing pad and the surface ofthe semiconductor wafer, and the surface of the semiconductor wafer ismade to rotate relative to the surface of the polishing pad.

In still another aspect of the present invention, an STI method isprovided in which a pad oxide layer and a silicon nitride layer aresequentially formed over a surface of a semiconductor substrate, aplurality of trenches are formed through the silicon nitride layer andthe pad oxide layer and into the semiconductor substrate, an insulatingoxide layer is formed within the plurality of trenches and over thesilicon nitride layer, the insulating oxide layer is subjected to CMP soas to remove the insulating oxide layer down to a level of siliconnitride layer, and the pad oxide layer and the silicon nitride layer arethen removed. In this STI method, the CMP includes contacting a surfaceof the insulating oxide layer with a surface of a polishing pad,supplying an aqueous solution containing abrasive particles anddifferent first and second passivation agents to an interface betweenthe surface of the polishing pad and the surface of the insulating oxidelayer, and rotating the surface of the semiconductor wafer relative tothe surface of the polishing pad.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the inventionwill become readily apparent from the detailed description that follows,with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a conventional chemical/mechanicalpolishing (CMP) apparatus;

FIGS. 2(a) through 2(d) illustrate stages of a conventional shallowtrench isolation (STI) process;

FIG. 3 shows the variation in the rate of oxide removal with respect tothe weight percentage of a removal rate accelerator added to an oxideslurry;

FIG. 4 shows a variation in both the oxide removal rate and the siliconnitride (SiN) removal rate as a function of a weight percentage of afirst passivation agent;

FIG. 5 shows a variation in both the oxide removal rate and the siliconnitride (SiN) removal rate as a function of a weight percentage of asecond passivation agent;

FIG. 6 shows a variation in both the oxide removal rate and the siliconnitride (SiN) removal rate as a function of a weight percentage of thesecond passivation agent in combination with a fixed amount of the firstpassivation agent;

FIG. 7 shows a variation in both the oxide removal rate, the siliconnitride (SiN) removal rate and oxide to SiN selectivity as a functionpH;

FIG. 8 is a process flow diagram of a CMP method of the presentinvention.

FIG. 9 is a process flow diagram of a shallow trench isolation method ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The chemical/mechanical polishing (CMP) slurry of the present inventionis an aqueous solution containing, for example, deionized water. Asdiscussed in detail herein, the present invention is at least partiallycharacterized by the discovery that the inclusion of two or moredifferent passivation agents, together with the abrasive particles ofthe CMP slurry, results in an unexpectedly high oxide to silicon nitride(SiN) selectivity.

Preferably, a first passivation agent is an anionic, cationic ornonionic surfactant, and a second passivation agent is a phthalic acid.During the CMP process, the first and second passivation agents resultin selective passivation of the SiN stop layer only, thus reducingetching of the SiN stop layer (which in turn increases selectivity).With respect to the first passivation agent, the anionic surfactant maybe selected from the group consisting of a carboxylic acid or its salt,a sulfuric ester or its salt, a sulfonic acid or its salt, and aphosphoric ester or its salt, the cationic surfactant may be selectedfrom the group consisting of a primary amine or its salt, a secondaryamine or its salt, a tertiary amine or its salt, and a quaternary amineor its salt, and the nonionic surfactant may be selected from the groupconsisting of a polyethyleneglycol type surfactant and a polyhydroxyalcohol type surfactant. In one example, the first passivation agent ispoly-vinyl sulfonic acid, and the second passivation agent is potassiumhydrogen phthalate.

A weight percentage of the first passivation agent in the aqueoussolution may be 0.001-10 wt %, and preferably 0.01-5 wt %. A weightpercentage of the second passivation agent in the aqueous solution maybe 0.001-1 wt %, and preferably 0.02-0.5 wt %.

Also, the aqueous solution forming the CMP slurry preferably includes aremoval rate accelerator. The removal rate accelerator may be oneselected from the group consisting of ammonium dihydrogen phosphate,potassium dihydrogen phosphate, bis(2-ethylhexyl) phosphate,2-aminoethyl dihydrogenphosphate, 4-chlorobenzenediazoniumhexafluorophosphate, nitrobenzenediazonium hexafluorophosphate, ammoniumhexafluorophosphate, bis (2,4 dichlorophenyl) chlorophosphate, bis(2-ethylhesyl) hydrogenphosphate, bis (2-ethylhexyl) phosphite, calciumfluorophosphate, diethyl chlorophosphate, diethyl chlorothiophosphate,potassium hexafluorophosphate, pyrophosphoric acid, tetrabutylammoniumhexafluorophosphate, and tetraethylammonium hexafluorophosphate. In oneexample, the removal rate accelerator is ammonium hydrogen phosphate,and a weight percentage of the ammonium hydrogen phosphate in theaqueous solution may be 0.001-10 wt %, and preferably 0.01-1 wt %.

The aqueous solution forming the CMP slurry further preferably includesa pH controller. For example, a pH of the aqueous solution may bebetween 2 and 6 inclusive. The aqueous solution may be an acid solutionsuch as sulfuric acid, chloric acid, phosphoric acid, nitric acid, orthe like, or the aqueous solution may be an alkaline solution such aspotassium hydroxide, sodium hydroxide, ammonium hydroxide, or the like.

The abrasive particles of the CMP slurry are preferably a metal oxideselected from the group consisting of ceria, silica, alumina, titania,zirconia and germania. In one example, the abrasive particles are ceriumoxide and a weight percentage of the abrasive particles in the aqueoussolution is 0.1-25 wt %.

As will be shown below, the CMP slurry of the present invention canprovide an oxide to silicon nitride selectivity of 50:1 and higher.

First, however, reference is made to FIG. 3 which illustrates theeffects of a removal rate accelerator, such as ammonium hydrogenphosphate. In particular, this figure shows the variation in the rate(in Å/min) of oxide removal with respect to the weight percentage amountof ammonium hydrogen phosphate added to the oxide slurry. In thisexample, the abrasive contained in the slurry is cerium oxide. As can beseen from FIG. 3, the CMP removal rate of the oxide increasessubstantially upon the addition of ammonium hydrogen phosphate to theoxide slurry.

Turning now to FIG. 4, the effect of combining a single passivationagent with a removal rate accelerator is shown. In particular, thisfigure shows a variation in both the oxide (PETEOS) removal rate and thesilicon nitride (SiN) removal rate as a function of a weight percentageof poly-vinyl sulfonic acid, which is an anionic surfactant, that isadded as a single passivation agent to the oxide slurry. In thisexample, the oxide slurry also includes the ammonium hydrogen phosphate(removal rate accelerator) discussed above in connection with FIG. 3. Ascan be seen from FIG. 4, the oxide removal rate increases somewhatrelative to that of FIG. 3. However, the oxide to SiN selectivity of theslurry is disadvantageously low.

Referring next to FIG. 5, the effect of combining a different singlepassivation agent with a removal rate accelerator is shown. Inparticular, this figure shows a variation in both the oxide (PETEOS)removal rate and the silicon nitride (SiN) removal rate as a function ofa weight percentage of potassium hydrogen phthalate, which is added as asingle passivation agent to the oxide slurry. In this example, the oxideslurry also includes the ammonium hydrogen phosphate (removal rateaccelerator) discussed above in connection with FIG. 3. As can be seenfrom FIG. 5, there are insubstantial changes in the oxide removal rate,and the silicon nitride removal rates decreases somewhat. Further, theoxide to SiN selectivity remains low.

Thus, as can be seen from FIGS. 4 and 5, the addition of a singlepassivation agent (either poly-vinyl sulfonic acid or potassium hydrogenphthalate) to the CMP slurry does not result a relatively high oxide toSiN selectivity.

As stated previously, the present invention is at least partiallycharacterized by the discovery that the inclusion of two or moredifferent passivation agents together with the abrasive particles of theCMP slurry results in an unexpectedly high oxide to silicon nitride(SiN) selectivity. This is demonstrated by way of example in FIG. 6. Inparticular, like FIG. 5, this figure shows a variation in both the oxide(PETEOS) removal rate and the silicon nitride (SiN) removal rate as afunction of a weight percentage of potassium hydrogen phthalate, whichis added as a passivation agent to the oxide slurry. Unlike the exampleof FIG. 5, however, the oxide slurry of FIG. 6 also includes anadditional passivation agent (poly-vinyl sulfonic acid), as well as theammonium hydrogen phosphate (removal rate accelerator). That is, theslurry of the example of FIG. 6 includes two different passivationagents (a first passivation agent of poly-vinyl sulfonic acid and asecond passivation agent of potassium hydrogen phthalate), as well as aremoval rate accelerator. Here, the percentage amount of the poly-vinylsulfonic acid is 0.05 wt %. As is readily apparent from the largedisparities in oxide and SiN removal rates shown in FIG. 6, asurprisingly high oxide to SiN CMP selectivity can be achieved by addingtwo different passivation agents (e.g., poly-vinyl sulfonic acid andpotassium hydrogen phthalate) to the CMP slurry.

As mentioned previously, the CMP slurry of the present inventionpreferably includes a pH controller. The pH controller can control thepH of the slurry by varying the composition of an acid solution such assulfuric acid, phosphoric acid, hydrochloric acid, nitric acid orcarboxylic acid, or an alkaline solution such as ammonium hydroxide orpotassium hydroxide, depending on the weight percentages of the removalrate accelerator and the first and second passivation agents that havebeen added to the slurry. In this embodiment, the pH of slurry iscontrolled using sulfuric acid and potassium hydroxide.

FIG. 7 shows the oxide and silicon nitride removal rates of a CMP slurryas a function of pH. Here, the slurry includes the removal rateaccelerator and the first and second passivation agents, and the pH ofthe resultant slurry was arbitrarily controlled using the pH controller.As can be seen from FIG. 7, the highest oxide to SiN selectivity isexhibited at pH 4.

To further enhance understanding of the present invention, a number ofdifferent test examples are described below.

<First Test Samples>

Three slurry samples were fabricated to estimate variations in thecharacteristics of the slurry with respect to an amount of phosphatecompound added to the slurry. In a sample wafer, which was a PETEOSblanket wafer, PETEOS was deposited to a thickness of 10000 Å on apolysilicon substrate, and a ceria polishing solution of 1 wt % was usedas a polishing agent. Polishing was performed in 6″ PRESI equipmentusing an IC1400 stack pad and an R200 carrier film from the RODELcompany, at a down pressure of 5 psi, a table speed of 65 rpm, a spindlespeed of 35 rpm and a slurry flow rate of 250 ml/min. The results ofestimation of the three slurry samples are shown in Table 1.

TABLE 1 ammonium hydrogen phosphate PETEOS removal rate sample (wt%) pH(Å/min) 1 0 4 1655 2 0.05 4 4602 3 0.1 4 4499

As can be seen from Table 1, when a small amount (about 0.05 wt %) ofammonium hydrogen phosphate, which is a phosphate compound, is added tothe slurry composition, the oxide removal rate substantially increases.

<Second Test Samples>

Five slurry samples were fabricated to estimate the oxide and SiNremoval rates and selectivity relative to the weight percentage of addedpoly-vinyl sulfonic acid, in a state where the amount of ammoniumhydrogen phosphate is fixed at 0.25 wt %. Each sample wafer was a PETEOSblanket wafer or a silicon nitride blanket wafer. When the sample waferwas a PETEOS blanket wafer, PETEOS was deposited to a thickness of 10000Å on a polysilicon substrate. When the sample wafer was a siliconnitride blanket wafer, high temperature oxide and silicon nitride aresequentially deposited to a thicknesses of 1000 Å and 2000 Å,respectively, on a polysilicon substrate. In the sample wafer, a ceriapolishing solution of 1 wt % was used as a polishing agent. Polishingwas performed in 6″ PRESI equipment using an IC1400 stack pad and anR200 carrier film from the RODEL company, at a down pressure of 5 psi, atable speed of 65 rpm, a spindle speed of 35 rpm and a slurry flow rateof 250 ml/min. The results of estimation of the five slurry samples areshown in Table 2.

TABLE 2 PETEO ammonium poly(vinyl S hydrogen sulfonic removal sam-phosphate acid) rate SiN removal ple (wt %) (wt %) pH (Å/min) rate(Å/min) selectivity 1 0 0 4 1242 542 2.3:1 2 0.25 0 4 3610 1099 3.3:1 30.25 0.01 4 3626 1125 3.2:1 4 0.25 0.05 4 4017 1256 3.2:1 5 0.25 0.1 44676 1401 3.3:1

As can be seen from Table 2, when the weight percentage of poly-vinylsulfonic acid is increased, the removal rates of both the oxide and theSiN also increase in a generally linear manner. As a result, there is noimprovement in the selectivity.

<Third Test Samples>

Five slurry samples were fabricated to estimate the oxide and SiNremoval rates and selectivity relative to the weight percentage of addedpotassium hydrogen phthalate, in a state where the amount of ammoniumhydrogen phosphate is fixed at 0.2 wt %.

Each sample wafer was a PETEOS blanket wafer or a silicon nitrideblanket wafer. When the sample wafer was a PETEOS blanket wafer, PETEOSwas deposited to a thickness of 10000 Å on a polysilicon substrate. Whenthe sample wafer was a silicon nitride blanket wafer, high temperatureoxide and silicon nitride were sequentially deposited to thicknesses of1000 Å and 2000 Å, respectively, on a polysilicon substrate. In thesample wafer, a ceria polishing solution of 1 wt % was used as apolishing agent. Polishing was performed in 6″ PRESI equipment using anIC1400 stack pad and an R200 carrier film from the RODEL company, at adown pressure of 5 psi, a table speed of 65 rpm, a spindle speed of 35rpm and a slurry flow rate of 250 ml/min. The results of estimation ofthe five slurry samples are shown in Table 3.

TABLE 3 PETEO- ammonium potassium S SiN hydrogen hydrogen removalremoval sam- phosphate phthalate rate rate ple (wt %) (wt %) pH (Å/min)(Å/min) selectivity 1 0 0 4 1242 542 2.3:1 2 0.2 0 4 2668 1206 2.2:1 30.2 0.01 4 2615 1155 2.3:1 4 0.2 0.1 4 2688 899 3:1 5 0.2 0.25 4 2744772 3.6:1

As can be seen from Table 3, when the weight percentage of potassiumhydrogen phthalate is increased, the oxide removal rate increasessomewhat, and the SiN removal rate decreases somewhat, resulting in anincrease in selectivity. Nevertheless, the selectivity is stillrelatively low.

<Fourth Test Samples>

In this instance, five slurry samples were fabricated to estimate theoxide and SiN removal rates and selectivity relative to the weightpercentage of added potassium hydrogen phthalate, which is a passivationagent, in a state where the weight percentage of ammonium hydrogenphosphate, which a removal rate accelerator, and poly-vinyl sulfonicacid, which is another passivation agent, are fixed at 0.05 wt %.

Each sample wafer was a PETEOS blanket wafer or a silicon nitrideblanket wafer. When the sample wafer was a PETEOS blanket wafer, PETEOSwas deposited to a thickness of 10000 Å on a polysilicon substrate. Whenthe sample wafer was a silicon nitride blanket wafer, high temperatureoxide and silicon nitride were sequentially deposited to thicknesses of1000 Å and 2000 Å, respectively, on a polysilicon substrate. In thesample wafer, a ceria polishing solution of 1 wt % was used as apolishing agent. Polishing was performed in 6″ PRESI equipment using anIC1400 stack pad and an R200 carrier film from the RODEL company, at adown pressure of 5 psi, a table speed of 65 rpm, a spindle speed of 35rpm and a slurry flow rate of 250 ml/min. The results of estimation ofthe five slurry samples are shown in Table 4.

TABLE 4 ammon- potass- ium poly- ium hydro- vinyl hydro- gen sul- genPETEOS SiN phos- fonic phtha- removal removal sam- phate acid late raterate select- ple (wt %) (wt %) (wt %) pH (Å/min) (Å/min) ivity 1 0.050.05 0 4 4556 1105 4.4:1 2 0.05 0.05 0.01 4 4557 1033 4.4:1 3 0.05 0.050.05 4 4465 59  76:1 4 0.05 0.05 0.1 4 4205 57  73:1 5 0.05 0.05 0.3 43582 63  57:1

As is readily apparent from Table 4, oxide to SiN selectivity issubstantially increased by the addition of different first and secondpassivation agents (such as poly-vinyl sulfonic acid and potassiumhydrogen phthalate) to the CMP slurry which also contains the removalrate accelerator. In fact, a selectivity of 50:1 or more can beachieved. This compares very favorably to conventional slurries whichtypically have a selectivity of around 4:1 or so.

<Fifth Test Samples>

In this case, three slurry samples were fabricated to estimate the oxideand SiN removal rates relative to different pH levels, in a state wherethe weight percentages of ammonium hydrogen phosphate, poly-vinylsulfonic acid and potassium hydrogen phthalate, were fixed at 0.05 wt %.

Each sample wafer was a PETEOS blanket wafer or a silicon nitrideblanket wafer. When the sample wafer was a PETEOS blanket wafer, PETEOSwas deposited to a thickness of 100000 Å on a polysilicon substrate.When the sample wafer was a silicon nitride blanket wafer, hightemperature oxide and silicon nitride were sequentially deposited tothicknesses of 1000 Å and 2000 Å, respectively, on a polysiliconsubstrate. In the sample wafer, a ceria polishing solution of 1 wt % wasused as a polishing agent. Polishing was performed in 6″ PRESI equipmentusing an IC1400 stack pad and an R200 carrier film from the RODELcompany, at a down pressure of 5 psi, a table speed of 65 rpm, a spindlespeed of 35 rpm and a slurry flow rate of 250 ml/min. The results ofestimation of the three slurry samples are shown in Table 5.

TABLE 5 PETEOS removal rate SiN removal rate PETEOS:SiN sample pH(Å/min) (Å/min) selectivity 1 4 5111 69  74:1 2 8 3667 1113 3.3:1 3 103852 1036 3.7:1

As can be seen from Table 5, as the pH of slurry increases, the removalrate of PETEOS decreases, while the removal rate of the silicon nitrideincreases substantially. Consequently, the selectivity of the PETEOSwith respect to SiN decreases substantially. Accordingly, in thisparticular embodiment, it has been determined that a slurry having a pHof 6 or less exhibits high selectivity. As such, selectivity can beespecially enhanced by the use of first and second passivation agents,together with a pH controller which results in a pH of 6 or less.

Turning now to the process flowchart of FIG. 8, a CMP process of thepresent invention will now be described. At step 802, a surface of asemiconductor wafer to be polished is made to contact the surface of apolishing pad. At step 804, an aqueous solution containing abrasiveparticles and different first and second passivation agents is suppliedto an interface between the surface of the polishing pad and the surfaceof the semiconductor wafer. Then, at step 806, the surface of thesemiconductor wafer is made to rotate relative to the surface of thepolishing pad.

As mentioned previously, the first passivation agent may be poly-vinylsulfonic acid, and the second passivation agent may be potassiumhydrogen phthalate. Also, a removal rate accelerator and/or a pHcontroller may be added to the aqueous solution defining the CMP slurry.

FIG. 9 is a process flow diagram of a shallow trench isolation method ofthe present invention. At step 902, a pad oxide layer is formed over asurface of a semiconductor substrate. Then, at step 904, a siliconnitride layer is formed over the pad oxide layer such that the pad oxidelayer is interposed between the semiconductor substrate and the siliconnitride layer. Next, at step 906, a plurality of trenches are formedwhich extend through the silicon nitride layer and the pad oxide layerand into the semiconductor substrate. At step 908, an insulating oxidelayer is formed within the plurality of trenches and over the siliconnitride layer. Next, at step 910, the insulating oxide layer is removeddown to a level of silicon nitride layer by being subjected to thechemical/mechanical polishing process described above in connection withFIG. 8. Again, the first passivation agent may be poly-vinyl sulfonicacid, and the second passivation agent may be potassium hydrogenphthalate. Also, a removal rate accelerator and/or a pH controller maybe added to the aqueous solution defining the CMP slurry. Then, at step912, the pad oxide layer and the silicon nitride layer are removed,resulting in a plurality of trench oxide regions in the surface of thesemiconductor substrate.

While the present invention has been described with reference to thedisclosed specific embodiments, it will be understood that modificationsmay be made without departing from the spirit of the invention. Thescope of the invention is not intended to be limited by the descriptionand examples set forth herein, but instead is to be defined by theappended claims.

1. A chemical mechanical polishing method comprising: contacting asurface of a semiconductor wafer with a surface of a polishing pad;supplying an aqueous solution containing abrasive particles a removalrate accelerator, and different first and second passivation agents toan interface between the surface of the polishing pad and the surface ofthe semiconductor wafer, wherein the first passivation agent is ananionic, cationic or nonionic surfactant; and, rotating the surface ofthe semiconductor wafer relative to the surface of the polishing pad toremove an oxide material on the semiconductor wafer.
 2. A chemicalmechanical polishing method comprising: contacting a surface of asemiconductor wafer with a surface of a polishing pad to remove an oxidematerial; supplying an aqueous solution containing abrasive particlesdifferent first and second passivation agents, wherein the firstpassivation agent is poly-vinyl sulfonic acid to an interface betweenthe surface of the polishing pad and the surface of the semiconductorwafer; and, rotating the surface of the semiconductor wafer relative tothe surface of the polishing pad.
 3. The chemical mechanical polishingmethod as recited in claim 2, wherein the supplied aqueous solutionfurther contains a pH controller and a removal rate accelerator.
 4. Thechemical mechanical polishing method as recited in claim 2, wherein thesupplied aqueous solution has a pH of between 2 and 6 inclusive andfurther contains ammonium hydrogen phosphate.
 5. A shallow trenchisolation method, comprising: forming a pad oxide layer over a surfaceof a semiconductor substrate; forming a silicon nitride layer over thepad oxide layer such that the pad oxide layer is interposed between thesemiconductor substrate and the silicon nitride layer; forming aplurality of trenches through the silicon nitride layer and the padoxide layer and into the semiconductor substrate; forming a insulatingoxide layer within the plurality of trenches and over the siliconnitride layer; subjecting the insulating oxide layer tochemical/mechanical polishing so as to remove the insulation oxide layerdown to a level of silicon nitride layer, wherein thechemical/mechanical polishing includes (a) contacting a surface of theinsulating oxide layer with a surface of a polishing pad, (b) supplyingan aqueous solution containing abrasive particles, a removal rateaccelerator, and different first and second passivation agents to aninterface between the surface of the polishing pad and the surface ofthe insulating oxide layer, wherein the first passivation agent is ananionic cationic or nonionic surfactant, and (c) rotating the surface ofthe semiconductor wafer relative to the surface of the polishing pad;and removing the pad oxide layer and the silicon nitride layer.
 6. Ashallow trench isolation method, comprising: forming a pad oxide layerover a surface of a semiconductor substrate; forming a silicon nitridelayer over the pad oxide layer such that the pad oxide layer isinterposed between the semiconductor substrate and the silicon nitridelayer; forming a plurality of trenches through the silicon nitride layerand the pad oxide layer and into the semiconductor substrate; forming aninsulating oxide layer within the plurality of trenches and over thesilicon nitride layer; subjecting the insulating oxide layer tochemical/mechanical polishing so as to remove the insulating oxide layerdown to a level of silicon nitride layer, wherein thechemical/mechanical polishing includes (a) contacting a surface of theinsulating oxide layer with a surface of polishing pad, (b) supplying anaqueous solution containing abrasive particles, poly-vinyl sulfonicacid, and potassium hydrogen phthalate to an interface between thesurface of the polishing pad and the surface of the insulating oxidelayer, and (c) rotation the surface of the semiconductor wafer relativeto the surface of the polishing pad; and removing the pad oxide layerand the silicon nitride layer.
 7. The chemical mechanical polishingmethod as recited in claim 6, wherein the supplied aqueous solutionfurther contains a pH controller and a removal rate accelerator.
 8. Thechemical mechanical polishing method as recited in claim 6, wherein thesupplied aqueous solution has a pH of between 2 and 6 inclusive andfurther contains ammonium hydrogen phosphate.
 9. The chemical mechanicalpolishing method as recited in claim 1, wherein the second passivationagent is a phthalic acid.
 10. The chemical mechanical polishing methodas recited in claim 1, wherein the supplied aqueous solution furthercontains a pH controller.
 11. The chemical mechanical polishing methodas recited in claim 1, wherein the supplied aqueous solution has a pH ofbetween 2 and 6 inclusive and further contains ammonium hydrogenphosphate.
 12. The chemical mechanical polishing method as recited inclaim 5, wherein the second passivation agent is a phthalic acid. 13.The chemical mechanical polishing method as recited in claim 5, whereinthe supplied aqueous solution further contains a pH controller.
 14. Thechemical mechanical polishing method as recited in claim 5, wherein thesupplied aqueous solution has a pH of between 2 and 6 inclusive andfurther contains ammonium hydrogen phosphate.
 15. A chemical mechanicalpolishing method comprising: contacting a surface of a semiconductorwafer with a surface of a polishing pad; supplying an aqueous solutioncontaining abrasive particles, poly-vinyl sulfonic acid, and potassiumhydrogen phthalate, to an interface between the surface of the polishingpad and the surface of the semiconductor wafer; and, rotating thesurface of the semiconductor wafer relative to the surface of thepolishing pad to remove an oxide material on the semiconductor wafer.16. The chemical mechanical polishing method as recited in claim 15,wherein the supplied aqueous solution further contains a pH controllerand a removal rate accelerator.
 17. The chemical mechanical polishingmethod as recited in claim 15, wherein the supplied aqueous solution hasa pH of between 2 and 6 inclusive and further contains ammonium hydrogenphosphate.